尽管城市与乡村有着很多不同之处，但它们是一个统一体，并不存在截然的界限，以下各要素中属于城乡服务联系的是( )。

A．公路网
B．交通服务形式
C．通信系统
D．经济联系

NAC，s rNetwork Access Control)role is to restrict network access to only compliant endpoints and (71) users．However，NAC is not a complete LAN (72) solution；additional proactive and (73) security measures must be implemented．Nevis is the first and only comprehensive LAN security solution thatcombines deeD security processing of every packet at 10Gbps，ensuring a high level of security plus applicationavailability and Derformance．Nevis integrates NAC as the first line of LAN security (74) ．In addition toNAC．enterFIrises need to implement role．based network access control as critical proactive security measuresreal．time，multilevel (75) inspection and microsecond threat containment

A．constructive
B．reductive
C．reactive
D．productive